Optical resolution for preparing optically active 1,4-dihydropyridine derivatives has been reported in Chem. Pharm. Bull., Vol. 37, p. 2225 (1989) and J. Med. Chem., Vol. 29, p. 2504 (1986). These known techniques, however, did not succeed to selectively obtain either only one of optical isomers as desired and are not therefore regarded industrially advantageous. Under the present situation, most of pharmaceuticals having a 1,4-dihydropyridine skeleton with an asymmetric carbon atom have been developed and put into medical use in the form of a racemate. A solution to this problem has thus been keenly demanded.